Current fabrication processes for trimming and drilling, and machining fuel seal grooves in composite and metallic aircraft panels utilize standard 3, 4, and 5 axis Numerically Controlled (NC) machine tools. Numerous machines of this type exist at aerospace companies which do not have integrated capabilities for machining operations to achieve specific seal groove widths/depths. Furthermore, these machines typically do not have integrated capabilities for performing drill countersinking operations to achieve specific countersink sizes/depths, and are relegated to drill-only operations which do not require specific depth control.
NC machines required to perform these types of processes are forced to integrate a complicated, expensive, and time consuming process of measuring and recording surface profile variations prior to actual machining and drilling. These recorded part surface variations are then used to adjust, or offset, the NC program to account for the deviations from the engineered nominal surface. NC Machines outfitted with the capability to perform these types of processes are substantially more expensive and complicated due to the added components and control hardware and software to operate the system. The lack of viable low-cost drill countersinking tools forces companies to convert these machines into accurate drill countersinking machines with expensive modifications and/or total machine replacement. This situation is prevalent throughout the aircraft industry, both in the commercial and military sectors.
Numerous machines exist today in production throughout the world without the capability to accurately machine seal grooves and drill countersink without substantial additional processes to accommodate the variations seen in composite and/or metallic panels, including surface profile variations. Numerically Controlled machines are programmed to move to a specific point in space without regard to where the actual part might be located. It is assumed that the part is located within a specific tolerance within the machine's work cell to achieve the desired level of accuracy during processing. Very small variations in machine accuracy and part location (i.e., as small as 0.001″—smaller than the thickness of a human hair) will result in seal groove widths and depths, and countersink diameters out of tolerance.
The primary issues with accurate seal groove machining and drill countersinking of composite or metallic parts is knowing or being able to reference the part's surface profile that will be machined, or the part's surface that will be drilled. All seal grooves and countersinks are referenced by this surface. There is currently no Commercial-Off-The-Shelf (COTS) seal groove machining system available in industry which can accurately machine a seal groove to a specified width and depth while adjusting to varying part surface profiles real time without some type of control system feedback or extensive measurement operations to identify the actual part surface profile.
In an expensive and complicated Automated Drilling Machine or Intelligent Drilling System the capability of sensing this surface location is incorporated into the machine and control system. This allows the machine to countersink to a depth relative to the sensed part surface. When the surface is located physically, or by non-contact methods, the drill countersink tool is fed a specific distance into the part relative to that surface to achieve the desired countersink diameter/depth.
Retrofitting existing machines without the specific designed-in countersinking and seal groove machining capabilities is very expensive and results in substantial machine downtime during retrofit. Most NC Machines have no or limited available control lines to die spindle for intelligent drilling systems. Integration costs for intelligent drilling systems are extremely costly and impact machine operations during installation/debugging.